Referring to FIG. 1, a front end circuit diagram of the prior art is showed. The front-end circuit 10 of the transceiver comprises an antenna 11, an amplifier 13, a mixer 15, and a local oscillator 17, wherein the antenna 11 is used for receiving a signal, such as a radio frequency (RF) signal or an analog signal, and transmitting the receiving signal to the amplifier 13 to be amplified, wherein the amplifier 13 is a low noise amplifier (LNA), thereafter, the amplified signal will be resulted to an intermediate frequency (IF) signal through the mixer 15 and the local oscillator 17, therefore, due to the previous frequency down conversion, the rear-end circuit of the transceiver can work according to the IF signal.
Generally, the gain of the amplifier can be modulated according to the strength value of the receiving signal through the antenna 11, for example, while the receiving signal is weaker, the gain of the amplifier 13 should be amplified properly, and thereby the rear-end circuit of the transceiver can work accordingly. On the contrary, while the receiving signal is stronger, the gain of the amplifier 13 should be reduced properly.
The gain of the amplifier 13 can be controlled according to the controller 19 connected with the amplifier 13, wherein the controller 19 is used for controlling the gain modulation according to the multi-level digital scaling, that is, the controller 19 would modulate the gain of the amplifier 13 according to the strength value of the receiving signal through the antenna 11.
However, there is a problem occurred while the gain of the amplifier 13 is modulated by the controller 19, that is, due to the controller 19 modulates the gain of the amplifier by the digital control signal, the transient response would be occurred since the gain is modulated to increase or decrease, therefore, the amplifier 13 would amplify the signal practically since the transient response has gone, thus, the operation performance of the front-end circuit 10 of the transceiver will be affected.
Furthermore, the value of the digital control signal would be determined by the strength value of amplified signal outputted from the amplifier 13, wherein the strength value of amplified signal will be detected by the rear-end circuit. However, the detection of the rear-end circuit has to be processed after the transient response has gone, otherwise, the detection thereof would be failure, such as the strength value of the transient response would be detected, thereafter, the gain modulation would be incorrect. Thus, due to the detection of the rear-end circuit has to be processed after the transient response has gone, and further, the gain will be modulated by the controller 19, therefore, the detection error might be occurred accordingly and the operation performance of the wireless transceiver would be reduced.